Kumi Naidoo is one of the world’s most celebrated, and innovative, social justice campaigners. In a broad-ranging interview, he reflects on four decades of activism, and the way he has worked with the law, from his time as a teenage anti-apartheid activist in the South African liberation movement, to his global stewardship of Greenpeace and Amnesty International. He recalls the way anti-apartheid activists in South Africa used court cases “not simply as an argument to the judges that were listening, but as an argument to the people, both to those who were oppressed, to say, ‘This is really bad, we must stand up and act against it’, and to those who were the oppressors, to say, ‘This system is unjust, unfair and untenable.” Following similar principles, he developed legal activism in two ways at Greenpeace: through civil disobedience and strategic litigation. But while the law is a critical tool for defending activists or for reforming society, the way change happens is through the kind of communication that leads to mass mobilization: “What we have to be really good at is communicating what we stand for to the largest number of people directly impacted.” Kumi explains his thinking, as one of the people who originated the phrase “climate justice”, in bringing a rights-based discourse to what was previously about science and land-use and economics: it communicated that global warming was a “human” issue with real impacts on real lives. He encourages young activists to follow law as a career, but warns “never to mistake access for influence.”